In the course of preparing images for display, such as, for example, movies, whether of the amateur or home type or professional type, videos, and the like, a camera typically would record one or more images of one or more scenes. The image information pertaining to the respective scene(s) may be processed and provided as image data. Processing may include, for example, arranging the data in a particular format for recording or for broadcasting. Various formats in which such data is stored and broadcast are known and new formats may be developed in the future. The image information and, thus, the image data may include, for example, respective R, G, B values, Y, U, V values, intensity, hue, saturation, and/or other information that may be used in displaying the image on a television, monitor or some other display. An example of a signal carrying such information is a video signal; another example is a digital signal. The present invention is not limited to the particular signal type or to the format of such signals.
One example of a format for image data storage is that in which the data representing the image characteristics of a frame, such as a momentary image of a scene, whether a “real” scene or an animated scene, may be stored in a storage medium, such as a DVD, CD, tape, computer hard drive, or some other memory; a number of sequential frames provide for a sequence of displayed images to display a motion picture, video, etc. One approach for storing image date for television display uses two fields to compose a frame, the image data for respective fields being stored in odd or even lines corresponding to the horizontal scan lines of a conventional television CRT (cathode ray tube) type of display. The present invention, as is described in detail below, is concerned with image data and is not limited to the format in which that image data is stored, such as, the number of fields from one to any larger number of fields per frame.
In the course of filming scenes, by using video camera, digital camera, film camera, or any other means to obtain images, illumination level ordinarily is determined by the amount of light incident on, reflected from or produced by objects in the scene or otherwise directed for pickup by the camera. The brightness characteristics of image information from a given scene as recorded by a camera may be adjusted by adjusting the camera aperture and/or shutter speed. Also, an optical filter may be used to change the appearance of a scene to a camera and, thus, characteristics of the image information obtained or recorded by the camera. However, there are a number of limitations on such filming techniques. For example, it may be rather inconvenient and time consuming to change optical filters during the course of filming a scene. Also, as illumination levels change, the effective sensitivity of the camera may be changed, whereby the amount of data perceived accurately by the camera may be diminished, e.g., loss of resolution, contrast, etc. Thus, there is a need to improve such resolution and contrast.
There are a number of different types of displays able to display images, such as movies, videos, still images, and the like. One type of display is a passive display. A passive display usually operates by modulating light that is provided thereto (incident light). An example of a passive display is a liquid crystal display, and another example of a passive display is known as a digital micro mirror device (DMD), such as that sold by Texas Instruments Incorporated. There are a number of liquid crystal display devices, such as, for example, those known as twisted nematic, supertwist, polymer disbursed liquid crystal (PDLC) also known as encap (NCAP), and ferroelectric; these are examples, and others may exist now or in the future. Another type of display is an active or light emitting display, which provides light output without the need for a separate illumination source or light source; examples include cathode ray tubes (CRT), electroluminescent displays (EL), plasma displays, and others that may exist now or in the future.
The displaying of a dark scene using a passive display encounters a disadvantage that ordinarily is not present for active displays. The problem has to do with reduced resolution and/or contrast of the displayed dark image. In an active display, such as a CRT, for example, when it is desired to display a dark scene, the intensity of the output light can be reduced by reducing input to individual pixels. The parts of the dark scene may be output at the reduced brightness or illumination level. However, the number of light producing pixels does not have to be reduced; all pixels of the CRT can be active so that resolution is maintained even though intensity of the light produced by the pixel phosphors, for example, may be reduced. A pixel sometimes is referred to as a picture element or pel, a phosphor dot in a monochrome display, especially a CRT type, or a group of three (red, green and blue) phosphor dots for a multicolor display, etc.
However, in a passive display, such as a liquid crystal display, a prior approach to reduce brightness of a displayed image or scene has been to reduce the number of pixels which are reflecting or transmitting light at a particular moment to form a relatively dark image. Such a reduction reduces the resolution and/or contrast of the display. Such a reduction also may adversely affect gamma characteristic of the display and/or of particular images provided by the display.
The pixels may be discrete pixels or may be blocks or areas where an optical signal or optical output can be developed by emission of an active display or by reflection or transmission of a passive display. The optical signal referred to may mean that light is “on” or provided as an output from the device or that the pixel has its other condition for not producing or providing a light output, e.g., “off”; and the optical signal also may be various brightnesses of light or shades of gray. The optical output or optical signal produced by a pixel may be a color or light of a particular color. These and other operating characteristics of displays are known and quite standard in the field of display technology.
The human eye has difficulty distinguishing between seeing or recognizing the difference between low and high brightness and contrast ranges. This difficulty is increased when the number of pixels is decreased and resolution is degraded. An approach to improve resolution and contrast in a passive display is described in U.S. Pat. No. 5,717,422, which is incorporated in its entirety by this reference. Other pending patent applications that describe approaches to increase resolution and contrast for a passive display, even when the display is showing a relatively dark image, are described in U.S. Pat. No. 6,184,969, issued Feb. 6, 2001, and co-pending U.S. patent application Ser. No. 09/676,915, filed Oct. 2, 2000, the entire disclosures of which are incorporated by this reference. The patents and patent application just mentioned describe controlling the intensity of light supplied to a light modulating passive display as a function of a brightness characteristic of the image being displayed.
In the '422 patent is disclosed a passive display apparatus, such as an LCD, and method for displaying images with high contrast by controlling the light input to the display to control brightness of the output image while operating respective pixels of the display to obtain good resolution and contrast without regard to the output brightness. Different color effects also can be obtained. As is described in the '422 patent, an image of a candle lit room would be relatively dim. The prior art passive displays would use a relatively small number of pixels to provide light that creates the image, whereas a relatively large number of pixels would be used to block light to give the effect of reduced intensity or dim room. In the invention of '422 patent, though, the number of pixels used to create the imagery does not have to be reduced to reduce light intensity or brightness of the image; rather, the intensity of the illuminating or incident light changes to diminish the brightness of the image. Therefore, image data would not be lost as brightness of an image is decreased. Thus, the amount of information that can be conveyed by the display in creating the image is increased over the capabilities in the prior art.
As an example of increased information provided by the invention of the '422 patent, one could obtain a gray scale of 100 shades of gray by using a passive display that provides 10 shades of gray and an illuminating source that provides light at 10 different levels; multiplying the display capability times the illuminating source capability yields 100 shades of gray. Gray scale capability can be increased further using a field sequential color display in which the illuminating light is provided sequentially as red, green, and blue light, each of which can be modulated separately by the display. Wide range of gray scale is advantageous in head mounted displays, e.g., virtual reality displays or other head mounted displays, where immersion in the image is desirable. Using features of the '422 patent, as were just described, high illumination can be provided a scene as it is filmed, yet the gray scale and contrast ratio of the image as actually displayed can be adjusted by adjusting the illuminating source for the display without loss of image data or with minimal loss of image data. Thus, a high contrast image can be presented. Also, adjustments can be made selectively to alter images so that, for example, a sunrise scene can be provided in which red portions of the image are enhanced and blue and green are minimized.
By separating the two functions of brightness (according to the intensity of the illuminating source) and image (based on operation of a passive display, e.g., a liquid crystal modulator), images can be adjusted to achieve a desired result. An example is to photograph a scene in daylight to get good resolution and contrast, and then by adjusting the illuminating source and/or the colors of the illuminating source, the impression of a moonlit scene, a candle lit environment, sunrise or sunset, etc., can be obtained.
Gamma is a characteristic or parameter that is used in the field of display technology. The Adobe Photoshop Version 7.0 software describes gamma in relation to the brightness of midtone values. As described there, the midtone values from black to white as produced by a monitor are nonlinear and, therefore, would be represented graphically as a curve rather than as a straight line. The slope of the curve halfway between black and white is what is defined by that software as the gamma value. Such software provides the possibility of adjusting gamma to improve the accuracy of a displayed image in reproducing the actual colors of a scene that is represented by the image. According to another consistent definition, gamma is the transfer function from the input light to the output image.
Gamma correction in the field of computer graphics also concerns control of overall brightness of an image. Gamma correction is desirable to obtain accurate displaying of images on a computer display or other display, display system, monitor or television. Note that the terms display, monitor, television and the like are used synonymously herein unless otherwise expressed or indicated by context. Varying the amount of gamma correction that is applied in a given display system may change brightness and also the ratios of red, green and blue colors, for example, that are displayed. Gamma correction is provided in conventional display systems in various ways to take into account that the intensity of a given pixel may have a non-linear relation to the drive signal, e.g., the drive voltage, for that pixel. As one example, for a conventional cathode ray tube monitor, the intensity to voltage response curve may be on the order of a 2.5 power function. Therefore, if for a given pixel an intensity voltage representing an intensity of i were to be delivered to the monitor, the monitor actually would provide intensity of i^2.5 (i to the 2.5 power). Therefore, the actual voltage supplied to the monitor must be corrected, i.e., gamma corrected, so the proper intensity is displayed. As is evident, gamma correction can be relatively complicated and in many instances the user of a display is not provided the ability manually to adjust gamma.
Color fidelity is the extent of accurate representation of the color characteristics of a scene as portrayed by a displayed image. Color fidelity may be degraded due to inaccurate illumination and/or gamma of a displayed image compared to the original scene. It would be desirable to improve color fidelity for passive displays and display systems.
It would be desirable to improve one or more of the contrast and resolution of and accuracy of image portrayal by passive displays. It also would be desirable to improve correction of gamma for passive displays. It also would be desirable to facilitate such improvements, adjustments and corrections.
A media processor is a device that is used in connection with televisions, computer displays, liquid crystal displays, and other displays to receive input signals representing image and/or other information and to provide an output in a format that can be displayed. Sometimes such a media processor is referred to as a media processor integrated circuit because the circuit and software functions thereof can be included in a single integrated circuit (or may be in several integrated circuits). It would be desirable to include in conjunction with a media processor integrated circuit one or more of the other features described herein.